Implant implantation unit and procedure for implanting the unit

ABSTRACT

The implant implantation unit ( 2 ), at a determined position in the tubular element ( 51 ) with a wall comprising a cavity ( 50 ), is pushed there by a catheter ( 60 ) and the unit comprises deformable feelers ( 31 ) to, under the control of remote activation elements ( 42 ), change from a stowed form to a deployed functional form, to detect the cavity ( 50 ) and position itself there with reference to the position of the cavity.

This application is a continuation of U.S. application Ser. No. 12/138,983, filed on Jun. 13, 2008, now pending, which is a continuation U.S. application Ser. No. 10/210,085, filed on Aug. 2, 2002, now abandoned, which applications are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The current invention relates to an implant implantation unit and to a procedure for fitting the unit in a tubular element.

The problem at the origin of the invention concerns the implantation of heart valves. Until recently this necessitated open heart surgical operations, with stages such as stopping the heart, the implementation of extra bodily blood circulation and restarting the heart after the implantation of replacement heart valves. These surgical operations are difficult and delicate and present mortal risks related to operating shocks.

BACKGROUND

Document U.S. Pat. No. 5,824,063 thus describes a unit carrying replacement heart valves, the unit comprising a tubular implant in synthetic material carrying internally a replacement valve in natural material.

Documents U.S. Pat. No. 5,855,601 and U.S. Pat. No. 5,868,783 describe new heart valve implantation methods, which offer the advantage of avoiding open heart surgery. These methods provide the implantation, by movement through the blood circulation system, of a heart valve replacement unit comprising a radially expandable intra-vascular cylinder carrying a biological valve internally. An inflatable part of a balloon catheter is placed inside the carrier cylinder and the implantation is done by introduction into a vein and movement as far as the failed valve using A catheter. A two dimensional image screen display allows the detection that the carrier cylinder has reached the required position and the cylinder is then dilated by inflating the balloon through the catheter and maintains its expanded shape. The balloon is then deflated and withdrawn with the catheter.

The carrier cylinder presents a sealed casing, which is thus forced against the artery wall, so as to avoid the blood flow bypassing the replacement valve.

However, when the aorta is involved this procedure is not applicable because the coronary arteries open close to the failed native valves, so that the carrier cylinder is likely to block them, provoking the death of the patient.

SUMMARY

The inventors of the present application have therefore thought of providing two corresponding openings in the wall of the carrier cylinder casing. However, so that these openings will be placed opposite the two coronaries, the position of the carrier cylinder in the aorta must be completely controlled. Monitoring on the screen allows the progress, or axial position, of the carrier cylinder to be checked, but the angular position wilt be neither visible nor controlled.

The applicants have therefore found a solution, described below, allowing the position of the carrier cylinder to be controlled.

They have therefore thought about the resolution of the more general problem of positioning an implant unit or transport vehicle in a tubular element with difficult access and for which imaging is insufficient or even impossible. The field of application could thus concern other fields than the medical, such as the petroleum or nuclear industries, for installing sensors, valves and other items. The scope of the present application must therefore not be considered as limited to the resolution of the original problem. In a more general way, the invention aims to allow, the placing, in a difficult to access location of a tubular element, of a unit intended to carry an implant, whatever the function of the implant.

To this end, the invention concerns in the first place a unit for the implantation in a determined position of a tubular element with a wall comprising a cavity, the unit being arranged to cooperate with means for driving the unit in the tubular element, a unit characterized by the fact that it comprises deformable feelers arranged so that, under the control of means for remote activation, it passes from a stowed to a deployed functional shape, to detect the cavity and position itself there with reference to the position of the cavity.

Thus, the unit can be made to advance blind and the feelers allow the automatic detection of the cavity and positioning at it.

The final required position can also be reached even through a contraction of the tubular element for example an access artery leading to an artery of larger diameter.

The invention also concerns a process, which is not surgical and without therapeutic aim, for implantation of the inventive unit, at a predetermined position in a tubular element presenting a wall comprising a cavity which procedure is characterized by the fact that

a user inserts the unit through an open end of the tubular element

he activates drive means to make the unit advance to a position before the determined position,

he commands the feeler remote activation means and, with the advance continuing,

he stops the action of the drive means when he detects a blockage of the advance, indicating that the feeler means are positioned in the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and advantages of the present invention will appear more clearly with the aid of the following description of a particular form of the realization of the inventive unit and a variant, as well as the procedure for using it, with reference to the attached drawing, in which:

FIG. 1 is a lateral cross section of the inventive unit, representing the feeler positioning and anchoring elements, associated with a cylinder carrying a valve prosthesis, the whole being covered by two removable concentric activation casings,

FIG. 2 corresponds to FIG. 1, the feeler positioning and anchoring elements having been deployed radially by axial withdrawal of the external casing,

FIG. 3 corresponds to FIGS. 1 and 2, with the carrier cylinder surrounded by positioning and anchoring feeler elements having been deployed radially alter axial withdrawal of the internal casing,

FIG. 4 is a lateral view of the carrier cylinder and the positioning and anchoring feeler elements,

FIG. 5 is a lateral perspective view of the positioning and anchoring feeler elements,

FIG. 6 is a schematic face view of the inventive unit, and

FIG. 7 is a schematic lateral section of the variant.

DETAILED DESCRIPTION

As shown in FIG. 1, the present implementation example corresponds to the medical problem, explained at the beginning, of implanting a functioning replacement valve for the native aorta valve. The valve implantation unit 10 comprises a carrier element 20 to hold the implant, joined to a plurality of feeler, or palpation, elements or fingers 30, 31, here regularly spaced angularly all around, for positioning and anchoring relative to relief features, specifically a cavity in the aorta wall, unit 10 being linked removably to a positioning catheter 60. Unit 10 is associated with two concentric sleeves 41, 42 for successive remote activation, by radial expansion, of feeler elements 30, 31 then the carrier element 20. The direction of movement of unit 10 is therefore towards the left in FIGS. 1 to 3. Reference 62 represents an axis of symmetry and the drive direction of unit 10 and catheter 60.

The implantation valve forms a prosthesis 1 comprising valve units 2 of the valve whose shape and size correspond perfectly, in the operating position, to those of the native aorta valves 50 (FIG. 2). The prosthesis 1 is fixed to the implant holding carrier vehicle element 20, here comprising a cylindrical mesh in a bio-compatible material such as steel, gold alloys and for preference as here, nitinol, which comprises a shape memory nickel-titanium alloy offering the ability to regain its shape after initial deformation, here by radial compression. The fixing of prosthesis 1 to the cylindrical nitinol mesh is made in well defined locations leaving free those regions that correspond to the valve units 2 after deployment from the stowed position of FIG. 2, as illustrated below in respect of FIG. 3.

FIG. 4 represents the cylindrical mesh 20 in the deployed form, carrying the valve units 2 also deployed internally, on which are connected the feeler elements 30, 31, here in the form of a generally cylindrical exterior ring of wire loops of which one (31) at least, here in fact three, protrudes laterally and towards the front, opposite the catheter 60. In this example, the loops 31 extend, in the deployed position, in a direction inclined at about 30 degrees towards the front (direction of movement towards the target position) relative to the axis 62 of the mesh 20 and the ring 30. The feeler elements 30, 31 are joined to the cylindrical mesh 20 in such a way that their axial and angular positions relative to it are perfectly defined. The assembly, cylindrical mesh 2 and feeler elements 30, 31, is here composed of the auto expandable bio-compatible material mentioned above.

The cylindrical carrier mesh 20 is here covered with an impermeable lateral casing intended to be pressed against the aorta wall to avoid bypassing by the blood circulation.

FIG. 5 shows the feeler elements 30, 31 in perspective. FIG. 6 is a schematic view, along the unit 10 axial direction, showing the three loops 31 protruding laterally from the tubular grid 20 that carries them, while the 2 valve units of the valve to be implanted are fixed internally to the carrier cylinder 20.

In addition, if necessary, an inflatable balloon, joined to the catheter 60, can here be placed inside the carrier cylinder 20, to be fed with liquid under pressure through catheter pipe 60 so as to cause or assist the radial expansion of the carrier cylinder 20 to the required deployed form.

As the feeler elements 30, 31 are made in a self expanding material such as nitinol, or an equivalent element forming an elastically protruding foot or finger, unit 10 is covered with an inhibition sleeve 42 to hold the feeler elements 30, 31 in a stowed position, the loops 31 being folded on the ring 30 and thus also on the mesh 20. Sleeve 42 extends to cover the catheter 60. A second sleeve 41, effectively the same length and without effect on the feeler elements 30, 31, is here similarly provided to hold the carrier cylinder 20 in the stowed position, so as to avoid unplanned deployment even in the absence of inflation of the balloon 3. The two sleeves 41, 42, are mounted concentrically on the catheter 60. The sleeves 41 and 42 are accessible from the end of catheter 60 opposite to the unit 10. Elements 3, 41, 42, and 60 comprise a functional catheter assembly separable from the unit 10, for the positioning and switching on this latter and the payload (2).

The two sleeves 41, 42 inhibit the radial deployment or the structure 20, 30, 31 until the latter reaches the region of the native aorta valve 50 to be functionally replaced, and thus allow the introduction of unit 10 into the blood circulation system, such as a reduced diameter incised artery. As indicated, the catheter 60, with balloon 3, is detachably joined to the implantation unit 10 so as to allow an axial advance of the implantation unit 10 in the blood circulation system up to the implantation location, and the withdrawal of the catheter assembly 3, 41, 42, 60.

To free itself, the catheter 60 comprises, in this example, at the fixed end of carrier cylinder 20, a spring effect clamp (not shown), with remotely controlled teeth, fitted to rotate radially, for connection to the unit 10 and has a sliding central remote control metal wire to axially push back the claw branches or teeth so as to separate them radially and so free the catheter 60 of the implantation unit 10 according to the sugar claw principle.

When the cylindrical mesh 20 is deployed, the pressure on the aorta internal wall is provided by the shape memory effect, which thus ensures the radial dilation of the prosthesis 1. The failed native valve unit 50 is flattened by being pressed by the tubular grid 20 against the aorta internal wall, each of the three loops 31 protruding lateraly having previously been engaged in one, specifically, of the three native valve units 50 and being similarly pressed to confirm its anchorage. The valve units 50 are thus clamped between the mesh 20, 30 and the respective loops 31.

The implantation procedure for the unit 10 described above, according to the preferred method of implementation, comprises the following steps. After insertion of the implantation unit 10 into the circulatory system, and after having pushed it using the catheter 60 to a position above the final target position, here precisely where the unit 10 arrives in the aorta, and so that a large diameter space is thus offered to it, the following stage consists of freeing the lateral loops 31, initially pressed against the stowed mesh 20, 30. The release of the loops 31 is done by withdrawing the external retention sleeve 42 (FIG. 2), that is to say withdrawn whilst maintaining the thrust on the catheter 60. The forward movement of the unit 10 continuing, the loops 31, being then protruded laterally towards the front with respect to the axial direction of forward movement, in opposition to the catheter 60, they form a sort of tripod and simultaneously penetrate the three respective native valves 50, effectively identical, comprising an arrangement of connection pockets in a complete ring with each extending over 120 degrees, filling in total the whole of the perimeter of the aorta internal wall 51. Each native valve unit 50 offers a rounded base.

Each lateral protrusion 31, turned towards the front, presses against the base of the native valve unit 50 concerned, in general in a point distant from the “lowest” point of the base, that is to say, the furthest from the catheter 60. This is therefore a partial stop because the axial advance of the unit 10 continues by thrust from the catheter 60, the axial thrust of the unit 10 causing it to side to the lowest point. The bottom of the valve unit 50 thus comprises a sort of inclined plane guidance track (not orthogonal to the axis (62) of the aorta) which, in reaction to the axial forward force, creates a circumferential reaction force causing the rotation of the unit 10 until the feeler loop considered 31 reaches the lowest point, which corresponds to a complete end wall (with tangential plane orthogonal to the axis (62) of the aorta 51), and thus corresponds to the final axial and angular position sought for the unit 10.

Each lateral protrusion 31, with rounded ends, here as a loop, so as to be able to slide in the bottom of the valve unit 50, thus comprises, by continuous cooperation with the variable depth rounded base of the native valves 50, means for rotational drive of the feeler elements 30, 31 and thus also of the cylindrical mesh 20, to which it is joined. However if the lateral protrusions 31 by chance bump against a native valve unit 50 commissure, the implantation unit 10 can be slightly withdrawn and the operator twists the catheter 60 so that it pivots angularly to be able to restart the positioning and anchoring operation.

The assembly, feeler elements 30, 31 and cylindrical mesh 20, being positioned axially and at an angle with respect to the specific relief of the aorta comprising the native valve units 50, it is then automatically positioned with respect to the two coronary openings (52) for which the axial and angular position with respect to the valve units 50 is determined and known, the valve unit−coronary axial distance evidently depending on the size of the patient.

In the case considered here in which the three native valves 50 form a circular circumference to the aorta wail extending over 360 degrees, a single lateral protrusion is sufficient to modulo 120 degrees positioning and anchoring the cylindrical mesh 20. As stated above, in a general case, there could only be one feeler 30, 31 working with a row of cavities or pockets covering all the circumference of the tubular element, or even a single pocket of cavity 50 only occupying a sector of the circumference and a plurality of feelers 30, 31 all around the unit 10 so that one of them fits in the cavity.

It will be noted that, in the present example, modulo 120 degrees positioning can be tolerated because the two coronaries (52) naturally effectively show this angle. If this was not the case, it would be necessary laterally to enlarge two openings or serrations 22 provided in the casing 21 so that they were positioned opposite the coronaries (52) (FIG. 4 and position marked on FIG. 3.), or again to feel, using the feelers 31, the coronaries (52) themselves, which also comprise cavities in the aorta 51, and not to sense the native valve units 50. This case corresponds to the variant described below.

Positioning thus having been effected, the following stage, as show in FIG. 3, consists of deploying the cylindrical mesh 20 carrying internally the valve units 2 by withdrawing the internal retaining sleeve 41, to consolidate the anchorage and change the valve units 2 to their operational form. For the clarity of the drawing, in particular the protrusions 31, the mesh 20 has been represented with a relatively small diameter, whereas in fact it matches that of the aorta 51, with a slight increase to ensure the required lateral pressure. In the same way, two protrusions 31 have been represented, although in fact they are separated by 120 degrees, with the plane of FIG. 3 only in reality cutting one. For this reason, only a single coronary has been drawn (52).

The three loops 31 protruding however provide by themselves a basic anchorage in the bottom of the pockets comprising the native valves 50 and ensure the positional stability of the prosthesis 1. After a flew weeks, fibrous tissue will cover the prosthesis 1, combining with the lateral protrusions 31 to further improve the fixing.

It will be noted however that, in the deployed position of the feeler elements 31, it is not necessary that their free ends should be firmly pressed against the aorta 51 wall. It is sufficient that their radial extension should be sufficient that they hook, in passing, onto the valve units 50. Because of this, when the feeler elements 31 are deployed, before the final position, the later axial translation of the unit 10, up to this position, is done without “hard” rubbing under pressure, of the part of the loops 31 on the aorta wall 51. The latter thus does not run any risk of damage due to scratching or piercing, the loops 31 being feelers, that follow the aorta wall 51 to detect the valve units 50. As described above, rounded feet or lugs can also be suitable.

The feeler loops 31 thus do not here have very firm anchoring of the unit 10 in the aorta 51 as their main function, because they do not aim to exert a large radial anchoring pressure. As indicated above, this is only a basic anchoring. It is then the radial deployment of the mesh 20 that creates, by shape memory, a definitive radial anchoring pressure that forces the mesh 20 under pressure against the aorta wall 51 and thus blocks any relative movement, such as the withdrawal of the unit 10 that could be due to blood flow, in a direction opposite to the insertion of the unit 10. The feeler elements t are then functionally superfluous. They however contribute to maintaining position by pinching the valve units 2. As the mesh offers a relatively high contact surface with the aorta 51, any risk of damaging the latter is excluded. The shape memory material allows the radial pressure exerted on the aorta 51 to be precisely determined, the diameter of the latter thus increased being then perfectly defined, which eliminates all risk of excessive radial stress.

The inventive procedure can be implemented in non-surgical manner and without therapeutic aims, to implant the unit 10 (or equivalent) in a determined position in a tubular elements offering a wall including a cavity, the procedure comprising the following stages:

a user inserts the unit (10) into an open end to the tubular element,

the user activates the drive means (60) (catheter, external magnet or other) to move the unit (10) up to a position upstream the determined position,

the user commands the feeler element (30,31) activation means (42) and, the forward motion continuing,

the user stops the activation of the drive means (60) when he detects a blockage of the advance, due to the fact that the feeler means (30,31) are positioned in the cavity.

To ease the drive of the unit 10, this one can be associated with a type of precursor rostrum 61 (FIGS. 1 to 3) forming a guide, in the form of a cylindrical element of a limited diameter, joined to the catheter 60.

It will be noted that the implantation unit according to the invention can, first, be implanted alone, without implant or payload, the latter being implanted later on the implantation unit according to the same principle. In a similar case, the inventive unit comprises means for receiving the second support, to come, of the implant, said means being arranged to ensure the positioning and anchorage, both axially, by stopping, and radially, with angular error correction means such as a finger or cavity provided to fit with an element of matching shape in the second support.

In the variant shown in FIG. 7, the implantation unit has the reference 110 and comprises functional elements similar to those of unit 10, with the same references preceded by the hundred 1, which have not however all been represented, with the aim of clarity. The cylindrical carrier element 120 is joined to a feeler element 131 which protrudes laterally and which has the same type of construction as the carrier element 120. In precise fashion, the feeler element 131 appears in the form of a cylinder, stowed radially in the rest position. When the unit 110 is pushed by the catheter 160, towards the bottom in FIG. 7, from a position above that shown, it engages in the coronary 52 when the free end is thus released from contact with the internal wall of the aorta 51.

The unit 110 thus comprises a type of fork that locks by stopping in the bifurcation between the aorta 51 and the coronary 52. When the end position is reached the two cylindrical elements 120, 131 are deployed by two balloons respectively and form a type of two fingered glove.

Thus, during the positioning phase, the feeler 131 presents a radially stowed form, thus with reduced diameter not risking blocking the coronary 52. Then the feeler 131 is deployed, by inflation of the associated remote control balloon, and constitutes a lining, or internal ‘casing’, pressed against the internal wall of the coronary 52 in accordance with the principle explained above for the carrier cylinder 20.

It will be noted that, as 120 and 131 each occupy a particular branch 51, 52, they can be considered as functionally equivalent, with the two principle functions if required. Each of them can in effect be a payload (2) carrier and can also be considered as being a feeler, because the aorta 51 can be considered (functionally in the context of the present invention) as being a cavity or branch with respect to the coronary 52. Thus the feeler means comprise a cylindrical element 131 arranged to change from a stowed form to a radially deployed form supported against a wall of the cavity, here the coronary 52, under the influence of remote control means (balloon and catheter 160),

To avoid the risks of movement of the feeler 131 into the coupling position to the coronary 52, due to an angular error that necessitates several attempts, it can be arranged for a guide wire to be passed into the coronary 52 and the upper part of the aorta 51, the unit 110 being threaded above it across the feeler 131 that is thus angularly oriented towards the coronary 52. Another guide wire can at the same time guide cylinder 120 into the aorta 51. 

1-10. (canceled)
 11. A method comprising: providing a semilunar valve prosthesis; placing the prosthesis in a body of a subject; and determining a correct rotational disposition of the prosthesis with respect to a semilunar valve site based on tactile feedback.
 12. The method according to claim 11, wherein providing the semilunar valve prosthesis comprises providing an aortic valve prosthesis.
 13. The method according to claim 11, wherein placing the prosthesis comprises placing the prosthesis without using any imaging techniques.
 14. A method comprising: placing a semilunar valve prosthesis at a native semilunar valve site; and causing the prosthesis to self-align with respect to the site by gently rotating the valve prosthesis.
 15. The method according to claim 14, wherein the semilunar valve prosthesis includes an aortic valve prosthesis, wherein the native semilunar valve site includes a native aortic valve site, and wherein placing comprises placing the aortic valve prosthesis at the native aortic valve site.
 16. The method according to claim 14, wherein causing the prosthesis to self-align comprises moving the prosthesis in an axial direction defined with respect to an axis of a downstream artery, while gently rotating the prosthesis.
 17. The method of claim 16, wherein the artery comprises an ascending aorta.
 18. The method according to claim 14, wherein gently rotating the prosthesis comprises moving the prosthesis in a proximal direction such that contact of the prosthesis with tissue of the native semilunar valve site causes the rotating.
 19. The method according to claim 14, wherein placing the prosthesis and causing the prosthesis to self-align comprise placing the prosthesis and causing the prosthesis to self-align without using any imaging techniques.
 20. The method according to claim 14, wherein causing the prosthesis to self-align comprises verifying that the prosthesis is properly aligned with respect to the semilunar valve site by attempting to rotate the prosthesis with respect to the semilunar valve site.
 21. The method according to claim 14, wherein the prosthesis is shaped so as to define one or more proximal engagement arms that are configured to be positioned at least partially within respective semilunar sinuses of the native semilunar valve site, and wherein causing the prosthesis to self-align comprises causing the engagement arms to self-align with respect to the respective semilunar sinuses.
 22. The method according to claim 21, wherein gently rotating the prosthesis comprises moving the prosthesis in a proximal direction such that contact of one or more of the engagement arms with tissue of the native semilunar valve site causes the rotating.
 23. The method according to claim 21, wherein causing the prosthesis to self-align comprises verifying that the engagement arms are properly placed with respect to the semilunar valve site by attempting to rotate the engagement arms with respect to the semilunar valve site.
 24. A method, comprising: placing a semilunar valve prosthesis at a native semilunar valve site, the prosthesis shaped so as to define one or more proximal engagement arms; attempting to position the engagement arms at least partially within respective semilunar sinuses of the native semilunar valve site; and verifying that the engagement arms are properly placed with respect to the semilunar valve site by attempting to rotate the engagement arms with respect to the semilunar valve site.
 25. The method according to claim 24, wherein the semilunar valve prosthesis includes an aortic valve prosthesis, wherein the native semilunar valve site includes a native aortic valve site, and wherein placing comprises placing the aortic valve prosthesis at the native aortic valve site.
 26. Apparatus comprising a prosthesis for implantation at a native semilunar valve of a native valve complex of a subject, the prosthesis comprising a support structure, which is configured such that a correct rotational disposition of the prosthesis with respect to the native semilunar valve can be determined based on tactile feedback.
 27. Apparatus comprising a prosthesis for implantation at a native semilunar valve of a native valve complex of a subject, the native valve complex having three semilunar sinuses and three native commissures, the prosthesis comprising a valve prosthesis support, which comprises a support structure comprising exactly three engagement arms that meet one another at three respective junctures, wherein the engagement arms are shaped so as to define three peak complexes at the three respective junctures, and three trough complexes, each of which is between two of the peak complexes, and wherein, upon implantation of the prosthesis, each of the engagement arms is at least partially disposed within a respective one of the semilunar sinuses, such that each of the peak complexes is disposed distal to a respective one of the native commissures, and each of the trough complexes is disposed at least partially within the respective one of the semilunar sinuses.
 28. The apparatus according to claim 27, wherein the native semilunar valve includes a native aortic valve of the subject, wherein the semilunar sinuses include respective aortic sinuses, and wherein, upon implantation of the prosthesis, each of the engagement arms is disposed at least partially within the respective one of the aortic sinuses.
 29. The apparatus according to claim 27, wherein the engagement arms are shaped such that each of the peak complexes includes exactly one peak at its respective one of the junctures.
 30. The apparatus according to claim 27, wherein the engagement arms are shaped such that each of the trough complexes includes exactly one trough.
 31. The apparatus according to claim 27, wherein the engagement arms are shaped so as to define exactly one trough between each two of the peak complexes.
 32. The apparatus according to claim 27, wherein the engagement arms are configured to touch respective transitions between the respective semilunar sinuses and respective native leaflet roots of the native valve complex, upon implantation of the prosthesis.
 33. The apparatus according to claim 27, wherein the valve prosthesis support, upon implantation of the prosthesis, does not press upon the native commissures of the native semilunar valve.
 34. The apparatus according to claim 27, wherein the prosthesis is configured to apply a radial force outwardly against the native semilunar valve.
 35. The apparatus according to claim 27, wherein the prosthesis is configured, upon implantation thereof, to embrace, without squeezing, leaflets of the native semilunar valve.
 36. The apparatus according to claim 27, wherein the valve prosthesis support is configured such that, upon implantation of the prosthesis, the valve prosthesis support does not fold over leaflets of the native semilunar valve.
 37. The apparatus according to claim 27, wherein the prosthesis is configured such that, upon implantation at the native valve complex, the engagement arms are aligned by rotation with respective ones of the semilunar sinuses.
 38. The apparatus according to claim 27, wherein each of the engagement arms is configured to engage a respective one of the semilunar sinuses upon implantation of the prosthesis.
 39. The apparatus according to claim 37, wherein each of the engagement arms is shaped to define a length, parallel to a longitudinal axis of the prosthesis, between (a) at least one of the junctures and (b) a contact point of one of the engagement arms that meets at the juncture with a sinus floor of the respective one of the semilunar sinuses upon implantation of the prosthesis, which length is greater than a distance of a native valve leaflet sinus to a free end of the native valve leaflet.
 40. The apparatus according to claim 27, wherein the prosthesis comprises a prosthetic valve comprising one or more prosthetic leaflets, wherein at least a portion of each of the prosthetic leaflets is configured to assume a closed position during diastole and an open position during systole, and wherein the at least a portion is not directly coupled to any of the engagement arms.
 41. The apparatus according to claim 40, wherein the prosthetic valve is coupled to the support structure such that at least a portion of an axial length of the prosthetic leaflets is distal to native valve leaflets of the native semilunar valve, upon implantation of the prosthesis.
 42. The apparatus according to claim 27, wherein the support structure is configured to serve as a distal fixation member, wherein the valve prosthesis support comprises a proximal fixation member, and wherein the proximal fixation member and the engagement arms of the distal fixation member are configured to axially sandwich the native valve complex from ventricular and downstream sides thereof, respectively, upon implantation of the prosthesis.
 43. A method for implanting a prosthesis at a native semilunar valve of a native valve complex of a subject, the native valve complex having three semilunar sinuses and three native commissures, the method comprising: providing the prosthesis including a valve prosthesis support, which valve prosthesis support includes a support structure comprising exactly three engagement arms that meet one another at three respective junctures, wherein the engagement arms are shaped so as to define three peak complexes at the three respective junctures, and three trough complexes, each of which is between two of the peak complexes; and implanting the prosthesis such that each of the engagement arms is at least partially disposed within a respective one of the semilunar sinuses, each of the peak complexes is disposed distal to a respective one of the native commissures, and each of the trough complexes is disposed at least partially within the respective one of the semilunar sinuses. 